We are interested in the symbiosis between Wolbachia endosymbionts and onchocercidae, a family of parasitic nematodes causing debilitating filariasis in tropical areas. Wolbachia are transmitted vertically, from the females to their progeny through the germline, like mitochondria. Wolbachia are essential for their host survival and fertility. Key questions: What are the transmission mechanisms of Wolbachia during the nematode life cycle? Why are the Wolbachia required for survival and fertility, in the filarial species they colonized?